Optical member, polyimide, method for manufacturing optical member, and method for producing polyimide

ABSTRACT

There is provided an optical member that can retain a high antireflection effect on a substrate for a long time. The optical member includes a laminated body that can reduce the reflection of light formed on a substrate surface, wherein at least one layer of the laminated body is a polyimide layer containing a polyimide film, and the polyimide contains a repeating unit represented by the following general formula (1), and a 1,4-cyclohexylene group in the main chain of R 2  in the general formula (1) contains 90% by mole or more of a trans-1,4-cyclohexylene group: 
     
       
         
         
             
             
         
       
         
         
           
             wherein R 1  denotes a tetravalent organic group, and R 2  denotes a divalent organic group having one or two or more 1,4-cyclohexylene groups in the main chain.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.13/581,098 filed Aug. 24, 2012, which is a national stage entry ofPCT/JP2011/054670 filed on Feb. 23, 2011, which claims priority toJapanese Patent Application No. 2011-022042 filed Feb. 3, 2011, JapanesePatent Application No. 2010-121000 filed May 26, 2010, and JapanesePatent Application No. 2010-043332 filed Feb. 26, 2010, all of which arehereby incorporated by reference herein in their entireties.

TECHNICAL FIELD

The present invention relates to an antireflective optical member and amethod for manufacturing the antireflective optical member and, moreparticularly, to an optical member suitable to stably achieve highantireflection performance from a visible region to a near-infraredregion for a long time, a polyimide, a method for manufacturing theoptical member, and a method for producing the polyimide.

BACKGROUND ART

Polyimides are used in electronic components and electrical machinerycomponents because of their high heat resistance and excellentelectrical insulating properties. Transparent polyimides having analiphatic structure are used also in liquid crystal display elements.However, the introduction of the aliphatic structure to imparttransparency to a polyimide can lower the heat resistance and themechanical characteristics of the polyimide. Thus, a polyimide havinghigh transparency, high heat resistance, and excellent mechanicalcharacteristics has been synthesized by introducing a specific alicyclicstructure (see PTL 1). A polyimide having high transparency, high heatresistance, and excellent mechanical characteristics has beensynthesized by using a substantially planar diamine, such astrans-1,4-cyclohexanediamine (see PTL 2). However, use oftrans-1,4-cyclohexanediamine made polymerization difficult because ofthe formation of a salt during polymerization. Thus, the formation of asalt must be reduced, for example, by silylation of the diamine.

It is also known that a polyimide produced using pyromellitic acid and4,4′-methylenebis(aminocyclohexane) has high transparency, high heatresistance, and excellent mechanical characteristics (see PTL 3).However, the polyimide produced by this method has low solubility. Thus,a film of the polyimide must be manufactured by heat treatment of a filmof a precursor, such as polyamic acid, at high temperature. This causesproblems, such as thermal damage to a substrate and degradation oftransparency because of the yellow coloration of the polyimide. Thus,there is a demand for a polyimide that is easy to synthesize, has hightransparency and heat resistance, and can be processed without causingthermal damage to neighboring members.

In an antireflective structure having a periodic fine structure having apitch less than or equal to a wavelength in a visible light region, itis known that the formation of a periodic fine structure having anappropriate pitch and height results in high antireflection performancein a wide wavelength range. A known method for forming a periodic finestructure includes the application of a film in which fine particleshaving a size less than or equal to the wavelength are dispersed. Inparticular, it is known that a textured structure formed of aluminumoxide boehmite grown on a glass substrate has a high antireflectioneffect. This textured structure formed of boehmite is produced by steamtreatment or hot-water immersion treatment of an aluminum oxide film,for example, formed by a liquid phase method (a sol-gel method) (see NPL1). However, exposure to water vapor or hot water can cause damage tothe glass substrate.

It is known that polyimides can be transparent, have a variablerefractive index, and protect a glass substrate from damage caused bywater or water vapor (see PTL 4). However, it is difficult to produce apolyimide that is easy to synthesize and has high transparency and heatresistance. In order to manufacture a low-reflectance optical member,there is a demand for an optical thin film that has small variations inthickness and optical properties.

A porous film that contains fine particles deposited on the surfacelayer as an antireflection coating and a metal oxide or halogenatedmetal layer formed by a method of growing boehmite on a substrate areconvenient and have high productivity and excellent optical performance.On the other hand, the porous film and the metal oxide or halogenatedmetal layer have low density and many voids. Thus, water from theoutside can easily reach the substrate, often causing erosion of thesubstrate or the elution of substrate components, such as alkali ions.Thus, there is a demand for a thin-film material that can be appliedbetween a porous film or a boehmite film and a substrate to improveantireflection performance and reduce damage to the substrate.Furthermore, there is a demand for a high-performanceantireflection-coated optical member without cracking or filmirregularities caused by a variation in film thickness or opticalproperties resulting from the effects of heat or water.

CITATION LIST Patent Literature

-   PTL 1 Japanese Patent Laid-Open No. 2002-161136-   PTL 2 Japanese Patent Laid-Open No. 2005-146072-   PTL 3 Japanese Patent Laid-Open No. 2007-313739-   PTL 4 U.S. Patent Application Publication 2008/0310026

Non Patent Literature

-   NPL 1 K. Tadanaga, N. Katata, and T. Minami: “Super-Water-Repellent    Al2O3 Coating Films with High Transparency”, J. Am. Ceram. Soc.,    80[4], 1040-1042 (1997)

SUMMARY OF INVENTION Technical Problem

In view of such background art, the present invention provides anoptical member that has a high antireflection effect on a substrate fora long time and a method for manufacturing the optical member. Thepresent invention also provides a polyimide that can retain transparencyafter processing into a membrane or film, has a sufficiently high glasstransition temperature, and is soluble in organic solvents, and a methodfor producing the polyimide.

Solution to Problem

An optical member that can solve the problems described above includes alaminated body that can reduce the reflection of light formed on asubstrate surface, wherein at least one layer of the laminated body is apolyimide layer containing a polyimide film, and the polyimide containsa repeating unit represented by the following general formula (1), and a1,4-cyclohexylene group in the main chain of R₂ in the general formula(1) contains 90% by mole or more of a trans-1,4-cyclohexylene group:

wherein R₁ denotes a tetravalent organic group, and R₂ denotes adivalent organic group having one or two or more 1,4-cyclohexylenegroups in the main chain.

A method for manufacturing an optical member that can solve the problemsdescribed above is a method for manufacturing an optical memberincluding a laminated body that can reduce the reflection of lightformed on a substrate surface, including

1) purifying a diamine represented by the following general formula (3)such that a 1,4-cyclohexylene group in the main chain of R₂ in thegeneral formula (3) contains 90% by mole or more of atrans-1,4-cyclohexylene group;

[Chem. 2]

H₂N—R₂—NH₂  (3)

wherein R₂ denotes a divalent organic group having one or two or more1,4-cyclohexylene groups in the main chain,

2) producing a polyimide containing a repeating unit represented by thefollowing general formula (1) by the reaction of the purified diaminewith an acid dianhydride represented by the following general formula(4) in a solvent;

wherein R₁ denotes a tetravalent organic group,

wherein R₁ and R₂ are as described above,

3) applying a solution containing the polyimide to the substrate or athin film formed on the substrate; and

4) drying and/or firing the applied solution containing the polyimide at100° C. or more and 250° C. or less to form a polyimide layer.

A polyimide that can solve the problems described above has a repeatingunit represented by the following general formula (1), wherein 90% bymole or more of a 1,4-cyclohexylene group in the general formula (1) hasa trans form:

wherein R₁ denotes a tetravalent organic group, and R₂ denotes adivalent organic group having one or two or more 1,4-cyclohexylenegroups in the main chain.

A method for producing a polyimide that can solve the problems describedabove includes

purifying a diamine represented by the following general formula (3)such that 90% by mole or more of a 1,4-cyclohexylene group in thegeneral formula (3) has a trans form;

[Chem. 6]

H₂N—R₂—NH₂  (3)

wherein R₂ denotes a divalent organic group having one or two or more1,4-cyclohexylene groups in the main chain,

producing a polyimide precursor by the reaction between the diaminerepresented by the general formula (3) purified and an acid dianhydriderepresented by the following general formula (4) in a solvent;

wherein R₁ denotes a tetravalent organic group,

producing a polyimide by the imidization of the polyimide precursor in asolvent; and

isolating the polyimide by removing the solvent.

The present invention can provide an optical member that can retain ahigh antireflection effect on a substrate for a long time. The presentinvention can also provide a method for manufacturing the opticalmember. The present invention can also provide a polyimide that canretain transparency after processing into a membrane or film, has asufficiently high glass transition temperature, and is soluble inorganic solvents, and a method for producing the polyimide.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of an optical member according to anembodiment of the present invention.

FIG. 2 is a schematic view of an optical member according to anotherembodiment of the present invention.

FIG. 3 is a graph illustrating the refractive index distribution of anoptical member according to an embodiment of the present invention.

FIG. 4 is a schematic view of an optical member according to anembodiment of the present invention.

FIG. 5 is a schematic view of an optical member according to anembodiment of the present invention.

FIG. 6 is a graph showing the relationship between the thickness of apolyimide thin film and a rate of increase in film thickness due to theimmersion of the film in hot water in Example 1 and Comparative Example1.

FIG. 7 is a graph showing DSC measurements of crude DADCM(4,4′-methylenebis(aminocyclohexane)) and purified DADCM in examples.

DESCRIPTION OF EMBODIMENTS

The present invention will be described in detail below.

An optical member according to an embodiment of the present inventionincludes a laminated body that can reduce the reflection of light formedon a substrate surface, wherein at least one layer of the laminated bodyis a polyimide layer containing a polyimide film, and the polyimidecontains a repeating unit represented by the following general formula(1), and a 1,4-cyclohexylene group in the main chain of R₂ in thegeneral formula (1) contains 90% by mole or more of atrans-1,4-cyclohexylene group:

wherein R₁ denotes a tetravalent organic group, and R₂ denotes adivalent organic group having one or two or more 1,4-cyclohexylenegroups in the main chain.

The polyimide can contain a repeating unit represented by the followinggeneral formula (2):

wherein R₁ denotes a tetravalent organic group, n denotes an integer inthe range of 0 to 2, R₃ to R₁₀ independently denote a hydrogen atom, ahalogen atom, a phenyl group, or a linear or cyclic alkyl, alkenyl, oralkynyl group having 1 to 6 carbon atoms, and R₁₁ and R₁₂ independentlydenote a hydrogen atom or a linear or cyclic alkyl group having 1 to 6carbon atoms.

FIG. 1 is a schematic view of an optical member according to anembodiment of the present invention. In FIG. 1, the optical memberaccording to this embodiment of the present invention includes apolyimide layer 2 containing a polyimide and a low-refractive indexlayer 3 on a surface of a substrate 1 in this order.

A laminated body 9 composed of the polyimide layer 2 and thelow-refractive index layer 3 can reduce the reflection of light on thesurface of the substrate 1. The polyimide layer is formed of a polyimidealone or a polyimide and a component other than the polyimide. Thecomponent other than the polyimide complements the polyimide and iscompatible with, can be mixed with, or can be dispersed in the polyimidewithin the bounds of not impairing the characteristics of the polyimide.

The formation of the polyimide layer 2 between the substrate 1 and thelow-refractive index layer 3 can produce a higher antireflection effectthan the formation of the low-refractive index layer 3 directly on thesubstrate 1. The thickness of the polyimide layer 2 is 10 nm or more and150 nm or less, preferably 20 nm or more and 80 nm or less, and dependson the refractive index of the substrate. The polyimide layer 2 having athickness below 10 nm has little antireflection effect. The polyimidelayer 2 having a thickness above 150 nm has a markedly reducedantireflection effect.

The polyimide contained in the polyimide layer 2 has a repeating unitrepresented by the following general formula (1):

wherein R₁ denotes a tetravalent organic group, and R₂ denotes adivalent organic group having one or two or more 1,4-cyclohexylenegroups in the main chain. Most of the 1,4-cyclohexylene group, morespecifically, 90% by mole or more of the 1,4-cyclohexylene group in themain chain of R₂ can be a trans-1,4-cyclohexylene group.

The divalent organic group having one or two or more 1,4-cyclohexylenegroups in R₂ in the polyimide can impart transparency and a lowrefractive index to the polyimide without lowering the heat resistanceof the polyimide. Although an aliphatic group in R₂ in the polyimide canreduce the refractive index of the polyimide, linear aliphatic groups oralicyclic groups other than the 1,4-cyclohexylene group lower the glasstransition temperature of the polyimide. 1,4-cyclohexylene can bedirectly bonded to the nitrogen atom of an imide ring in the polyimide.The polyimide can contain a repeating unit represented by the followinggeneral formula (2):

wherein R₁ denotes a tetravalent organic group, n denotes an integer inthe range of 0 to 2, R₃ to R₁₀ independently denote a hydrogen atom, ahalogen atom, a phenyl group, or a linear or cyclic alkyl, alkenyl, oralkynyl group having 1 to 6 carbon atoms, and R₁₁ and R₁₂ independentlydenote a hydrogen atom or a linear or cyclic alkyl group having 1 to 6carbon atoms.

The polyimide may further have a repeating unit represented by thefollowing general formula (5).

wherein R₁ denotes a tetravalent organic group, R₁₁ to R₁₄ independentlydenote a hydrogen atom, a phenyl group, or an alkyl, alkenyl, or alkynylgroup having 1 to 4 carbon atoms, R₁₁ to R₁₄ may be the same ordifferent, R₁₅ and R₁₆ independently denote a phenylene group or analkylene group having 1 to 4 carbon atoms, R₁₅ and R₁₆ may be the sameor different, and n denotes an integer in the range of 0 to 6.

The repeating unit represented by the general formula (5) can improvethe solubility of the polyimide. The repeating unit represented by thegeneral formula (5) can also improve the adhesion of a film made of thepolyimide.

A 1,4-cyclohexylene group can be introduced into R₂ in the polyimide byusing a diamine represented by the following general formula (3) havinga 1,4-cyclohexylene group or a derivative of the diamine as a monomer:

[Chem. 13]

H₂N—R₂—NH₂  (3)

wherein R₂ denotes a divalent organic group having one or two or more1,4-cyclohexylene groups in the main chain.

A diamine represented by the following general formula (6) or aderivative thereof can be used as a monomer:

wherein R₃ to R₁₀ independently denote a hydrogen atom, a halogen atom,a phenyl group, or a linear or cyclic alkyl, alkenyl, or alkynyl grouphaving 1 to 6 carbon atoms, and R₁₁ and R₁₂ independently denote ahydrogen atom or a linear or cyclic alkyl group having 1 to 6 carbonatoms.

Examples of the diamine having a 1,4-cyclohexylene group include, butare not limited to, 1,4-cyclohexanediamine,1,4-bis(aminomethyl)cyclohexane, 4,4′-methylenebis(aminocyclohexane),4,4′-methylenebis(1-amino-2-methylcyclohexane),2,2-bis(4-aminocyclohexyl)propane, 4,4′-bicyclohexylamine, andα,α′-bis(4-aminocyclohexyl)-1,4-diisopropylcyclohexane.

The diamine having a 1,4-cyclohexylene group is generally synthesized bythe hydrogenation of an aromatic diamine. The diamine synthesizedcontains a mixture of a trans-1,4-cyclohexylene group and acis-1,4-cyclohexylene group due to cis-trans isomerization. For example,a diamine having one 1,4-cyclohexylene group, such as1,4-cyclohexanediamine, contains a mixture of a structural isomer onlyhaving a trans form and a structural isomer only having a cis form. Adiamine having two 1,4-cyclohexylene groups, such as4,4′-methylenebis(aminocyclohexane), contains a mixture of a structuralisomer only having the trans form, a structural isomer only having thecis form, and a structural isomer (or stereoisomer) having one transform and one cis form.

Thus, a polyimide synthesized using the diamine having a1,4-cyclohexylene group described above without purification containsboth the trans-1,4-cyclohexylene group and the cis-1,4-cyclohexylenegroup. The heat resistance and the mechanical characteristics of thepolyimide depend on the ratio of the structural isomer having the transform to the structural isomer having the cis form.

The expression “most of the 1,4-cyclohexylene group in the polyimide hasthe trans form” indicates that the 1,4-cyclohexylene group in thepolyimide skeleton has the trans form alone or a mixture of the transform and a small amount of cis form. The polyimide in which most of the1,4-cyclohexylene group has the trans form has a higher glass transitiontemperature (Tg) than a polyimide in which most of the 1,4-cyclohexylenegroup has the cis form. Thus, a film made of the polyimide in which mostof the 1,4-cyclohexylene group has the trans form has a higher strength.

The polyimide layer 2 has a very small thickness of 100 nm or less. Achange as small as several nanometers in the thickness of the polyimidelayer 2 therefore results in deterioration of the optical properties ofan optical member according to an embodiment of the present invention.Since a thin film having such a thickness has a lower density than thinfilms having larger thicknesses, the thin film absorbs water in themanufacturing process or in the environment, causing an increase in filmthickness and variations in refractive index. This can cause unevensurface reflectance or cracking of an optical member. In the case thatmost of the 1,4-cyclohexylene group in the polyimide has the trans form,the polyimide having a thickness of 100 nm or less has smallervariations in thickness or refractive index resulting from moistureabsorption. This causes smaller variations in the optical properties ofan optical member according to an embodiment of the present invention.This is probably because the trans-1,4-cyclohexylene group in thepolyimide can be stacked on top of each other and thereby prevent waterintrusion.

The polyimide in R₂ in which most of the 1,4-cyclohexylene group has thetrans form is produced by using a diamine only having thetrans-1,4-cyclohexylene group as a monomer. The diamine is produced bythe purification of a mixture of structural isomers. The diamine onlyhaving the trans-1,4-cyclohexylene group can be isolated from a mixtureof structural isomers by the recrystallization of only ahigh-crystallinity trans form in a solvent, distillation under reducedpressure utilizing different boiling points of the isomers, extractionor washing utilizing different solubilities of the isomers in aparticular solvent, or chromatography.

However, it is difficult to completely isolate the diamine only havingthe trans-1,4-cyclohexylene group by these methods, and a small amountof diamine having the cis-1,4-cyclohexylene group remains. Thus,isolation conditions must be optimized or isolation procedures must berepeatedly performed so that most of the 1,4-cyclohexylene group has thetrans form.

It is desirable that the 1,4-cyclohexylene group in the main chain of R₂in the general formula (1) contain 90% by mole or more, preferably 93%by mole or more and 100% by mole or less, of the trans-1,4-cyclohexylenegroup. More specifically, the trans/cis ratio of the 1,4-cyclohexylenegroup in the polyimide may be at least 9/1 (mol/mol). The trans/cisratio lower than 9/1 results in insufficient prevention of waterintrusion and a marked increase in film thickness. Thus, the trans/cisratio of the 1,4-cyclohexylene group in the diamine having the1,4-cyclohexylene group corresponding to the polyimide skeleton can alsobe at least 9/1 (mol/mol).

The polyimide is synthesized by the polyaddition reaction between thediamine represented by the general formula (3) in which most of the1,4-cyclohexylene group has the trans form and the acid dianhydriderepresented by the general formula (4) and a dehydration condensationreaction (imidization reaction). Thus, the type of tetravalent organicgroup of R₁ in the general formula (1) is determined in accordance withthe type of the acid dianhydride represented by the following generalformula (4):

wherein R₁ denotes the tetravalent organic group.

The R₁ can be a tetravalent organic group represented by any of thefollowing general formulae (7) to (11).

Examples of the acid dianhydride used in the synthesis of polyimidesinclude, but are not limited to, aromatic acid dianhydrides, such aspyromellitic acid anhydride, 3,3′-biphthalic acid anhydride,3,4′-biphthalic acid anhydride, 3,3′,4,4′-benzophenonetetracarboxylicacid dianhydride, 3,3′,4,4′-diphenylsulfonetetracarboxylic aciddianhydride, 4,4′-(hexafluoroisopropylidene)diphthalic acid anhydride,and 4,4′-oxydiphthalic acid dianhydride, and aliphatic aciddianhydrides, such as meso-butane-1,2,3,4-tetracarboxylic aciddianhydride, 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride,1,2,3,4-cyclopentanetetracarboxylic acid dianhydride,1,2,4,5-cyclohexanetetracarboxylic acid dianhydride,bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride,bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic acid dianhydride,bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic acid dianhydride,5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylicanhydride, and4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylicanhydride. In order to improve the solubility, coating performance, andtransparency of polyimides, the acid dianhydride may be3,3′,4,4′-diphenylsulfonetetracarboxylic acid dianhydride,4,4′-(hexafluoroisopropylidene)diphthalic acid anhydride,meso-butane-1,2,3,4-tetracarboxylic acid dianhydride,bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic acid dianhydride,bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic acid dianhydride,5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylicanhydride, or4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylicanhydride.

In addition to the diamine in which most of the 1,4-cyclohexylene grouphas the trans form, one or more other diamines may be used in thepolymerization. In order to achieve high adhesion to an inorganicsubstrate, such as glass, and a low refractive index, a diaminerepresented by the general formula (12) may be used.

wherein R₁₁ to R₁₄ independently denote a hydrogen atom, a phenyl group,or an alkyl, alkenyl, or alkynyl group having 1 to 4 carbon atoms, R₁₁to R₁₄ may be the same or different, R₁₅ and R₁₆ independently denote aphenylene group or an alkylene group having 1 to 4 carbon atoms, R₁₅ andR₁₆ may be the same or different, and n denotes an integer in the rangeof 0 to 6.

Examples of the alkyl group having 1 to 4 carbon atoms include, but arenot limited to, a methyl group, an ethyl group, a propyl group, anisopropyl group, a butyl group, an isobutyl group, a sec-butyl group,and a tert-butyl group. Examples of the alkenyl group include, but arenot limited to, an ethenyl group and an allyl group. Examples of thealkynyl group include, but are not limited to, an ethynyl group and apropargyl group. Examples of the alkylene group having 1 to 4 carbonatoms include, but are not limited to, a methylene group, an ethylenegroup, an ethylidene group, a propylene group, an isopropylidene group,and a butylene group.

Specific examples of the diamine represented by the general formula (12)include, but are not limited to, organosiloxane diamines. Examples ofthe organosiloxane diamines include, but are not limited to, diamineshaving a diorganosiloxane group, such as1,3-bis(3-aminopropyl)tetramethyldisiloxane,1,4-bis(3-aminopropyldimethylsilyl)benzene, and dimethylsiloxaneoligomers having an amino group at both ends.

Polyimides having an organosiloxane group through an organosiloxanediamine have higher transparency, a lower refractive index, and narroweroptical dispersion than polyimides only having a hydrocarbon group.Polyimides only having an organosiloxane group are highly hydrophobicand have a low Tg because of their flexible structure. Films formed ofsuch polyimides are therefore brittle. However, a combined use of arepeating unit having the trans-1,4-cyclohexylene group and a repeatingunit having the organosiloxane group can provide a polyimide having alow refractive index and narrow optical dispersion without lowering theTg of the polyimide. The combined use can also impart high solubility inorganic solvents to the polyimide. The ratio of the amount of diaminerepresented by the general formula (12) to the amount of diaminerepresented by the general formula (3) used in the reaction describedabove may be 0.05 or more and 1 or less (mol/mol). The ratio of theamount of acid dianhydride represented by the general formula (4) to thetotal amount of diamine represented by the general formula (3) anddiamine represented by the general formula (12) used in the reactiondescribed above may be 0.94 or more and 1.06 or less (mol/mol). If theseratios fall outside these ranges, the polymerization proceedsinsufficiently, and an amino group or a carboxy group remains at an endof the polyimide, possibly causing moisture absorption or coloring ofthe polyimide.

Examples of a third diamine for use in the synthesis of the polyimideother than diamines in which most of the 1,4-cyclohexylene group has thetrans form include, but are not limited to, aromatic diamines, such asm-phenylenediamine, p-phenylenediamine, 3,4′-diaminodiphenylmethane,4,4′-diaminodiphenylmethane, 4,4′-diamino-3,3′-dimethyldiphenylmethane,o-tolidine, m-tolidine, 4,4′-diaminobenzophenone,1,1-bis(4-aminophenyl)cyclohexane, 3,4′-diaminodiphenyl ether,4,4′-diaminodiphenyl ether, 1,4-bis(4-aminophenoxy)benzene,1,3-bis(4-aminophenoxy)benzene,2,2-bis[4-(4-aminophenoxyl)phenyl]propane,4,4′-bis(4-aminophenoxy)biphenyl, bis[4-(4-aminophenoxyl)phenyl]sulfone,4,4′-bis(3-aminophenoxy)biphenyl, bis[4-(4-aminophenoxyl)phenyl]sulfone,9,9-bis(4-aminophenyl)fluorene, 9,9-bis(4-amino-3-methylphenyl)fluorene,9,9-bis(4-amino-3-fluorophenyl)fluorene,2,2-bis(4-aminophenyl)hexafluoropropane,2,2-bis(3-aminophenyl)hexafluoropropane,2,2-bis[4-(4-aminophenoxyl)phenyl]hexafluoropropane, and2,2′-bis(trifluoromethyl)benzidine. Polyimides produced by thecopolymerization with a diamine having an aromatic group can have arefractive index in the range of 1.5 to 1.7.

In particular, a combination with a diamine having a 1,4-cyclohexylenegroup and/or a diamine having an organosiloxane group allows widecontrol of the refractive index. Thus, 4,4′-bis(3-aminophenoxy)biphenyl,9,9-bis(4-aminophenyl)fluorene, 9,9-bis(4-amino-3-methylphenyl)fluorene,and 9,9-bis(4-amino-3-fluorophenyl)fluorene can be used.

Diamines having a linear or branched aliphatic group, such as1,4-diaminobutane, 1,5-diaminopentane, and 1,3-cyclohexanediamineunfavorably reduce the Tg of the polyimide.

The refractive index ni of the polyimide layer 2, the refractive indexnb of the substrate 1, and the refractive index ns of the low-refractiveindex layer 3 can satisfy the relationship of nb≧ni≧ns. The refractiveindex ns of the low-refractive index layer 3 may continuously increasefrom the top toward the substrate. In this case, the refractive index nsof the low-refractive index layer 3 is considered as the refractiveindex on the substrate side. A diamine only having thetrans-1,4-cyclohexylene group may be used in combination with 90% bymole or less of another diamine within the refractive index rangedescribed above.

The amount of the third diamine may be 50% by mole or less of the totalamount of diamine represented by the general formula (3) and/or diaminerepresented by the general formula (12) and the third diamine used inthe reaction described above. The amount of the third diamine largerthan 50% by mole may result in low transparency or an excessively highrefractive index.

A method for manufacturing an optical member according to an embodimentof the present invention is a method for manufacturing an optical memberincluding a laminated body that can reduce the reflection of lightformed on a substrate surface. This method includes

1) purifying a diamine represented by the following general formula (3)such that a 1,4-cyclohexylene group in the main chain of R₂ in thegeneral formula (3) contains 90% by mole or more of atrans-1,4-cyclohexylene group,

[Chem. 18]

H₂N—R₂—NH₂  (3)

wherein R₂ denotes a divalent organic group having one or two or more1,4-cyclohexylene groups in the main chain,

2) producing a polyimide containing a repeating unit represented by thefollowing general formula (1) by the reaction of the purified diaminewith an acid dianhydride represented by the following general formula(4) in a solvent,

wherein R₁ denotes a tetravalent organic group,

wherein R₁ and R₂ are as described above,

3) applying a solution containing the polyimide to the substrate or athin film formed on the substrate, and

4) drying and/or firing the applied solution containing the polyimide at100° C. or more and 250° C. or less to form a polyimide layer.

The method for manufacturing an optical member according to anembodiment of the present invention may further include

5) applying a precursor sol of aluminum oxide to the outermost surfaceof the laminated body,

6) drying and/or firing the applied precursor sol of aluminum oxide at100° C. or more and 250° C. or less to form an aluminum oxide film, and

7) immersing the aluminum oxide film in hot water to form a texturedstructure formed of plate crystals mainly composed of aluminum oxide.

A method for producing a polyimide according to an embodiment of thepresent invention will be described below.

In the synthesis of a polyimide, a diamine having one or two or more1,4-cyclohexylene groups represented by the general formula (3) ispurified by the method described above to produce a diamine in whichmost of the 1,4-cyclohexylene group has the trans form. The resultingdiamine is reacted with an acid dianhydride represented by the generalformula (4) in a solvent to produce a polyamic acid solution. Inaddition to the diamine in which most of the 1,4-cyclohexylene group hasthe trans form, a diamine represented by the general formula (12) and/orthe third diamine, such as an aromatic diamine, may also be reacted withan acid dianhydride represented by the general formula (4) in a solventto produce a polyamic acid solution. The imidization of the resultingpolyamic acid in a solution yields a polyimide. The polyimide may beisolated by removing the solvent.

The ratio of the amount of acid dianhydride represented by the generalformula (4) to the amount of diamine used in the reaction describedabove can be 0.94 or more and 1.06 or less (mol/mol).

The solvent for use in the synthesis of the polyimide may be any solventthat can dissolve the polyamic acid and the polyimide, for example, anaprotic polar solvent, such as N,N-dimethylformamide,N,N-dimethylacetamide, or N-methyl-2-pyrrolidone.

The imidization converts the polyamic acid into the polyimide bycyclodehydration. The imidization may be performed by heating at 25° C.or more and 120° C. or less in the presence of a tertiary amine, such aspyridine or triethylamine, and acetic anhydride or by azeotrope withxylene at 150° C. or more.

After the polyimide synthesis, the polyimide solution may be directlyused in the latter process. Alternatively, the polyimide solution may bepoured into a poor solvent to precipitate a polyimide powder, which isfiltered off, dried, and dissolved in a solvent again. In the lattercase, precipitation in an alcohol can remove unreacted monomers andvarious chemicals used in the imidization. The polyimide solution or theisolated polyimide powder may be dried at 50° C. or more and 150° C. orless in the atmosphere or under reduced pressure to remove the solvent.

The imidization rate of the polyimide is preferably 90% or more, morepreferably 93% or more and 99% or less. The imidization rate lower than90% tends to result in an increase in the water absorption rate of thepolyimide, causing variations in film thickness or refractive index.

A polyimide soluble in organic solvents according to an embodiment ofthe present invention may be dissolved again in an organic solventbefore use. Examples of the organic solvent include, but are not limitedto, ketones, such as 2-butanone, methyl isobutyl ketone, cyclopentanone,and cyclohexanone; esters, such as ethyl acetate, n-butyl acetate,ethylene glycol monomethyl ether acetate, propylene glycol monomethylether acetate, ethyl lactate, and γ-butyrolactone; ethers, such astetrahydrofuran, dioxane, diisopropyl ether, dibutyl ether, cyclopentylmethyl ether, and diglyme; aromatic hydrocarbons, such as toluene,xylene, and ethylbenzene; chlorinated hydrocarbons, such as chloroform,methylene chloride, and tetrachloroethane; and others, such asN-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide,dimethyl sulfoxide, and sulfolane.

In particular, a polyimide soluble in organic solvents according to anembodiment of the present invention may be dissolved in at least twosolvents selected from N,N-dimethylacetamide, cyclopentanone,cyclohexanone, propylene glycol monomethyl ether acetate, ethyl lactate,and γ-butyrolactone at a concentration of 5% by weight or more.

It is desirable that a repeating unit having the trans-1,4-cyclohexylenegroup in the repeating unit represented by the general formula (1) in apolyimide according to an embodiment of the present invention be 25% bymole or more and 90% by mole or less, preferably 30% by mole or more and95% by mole or less, of all the repeating units of the polyimide. Atless than 25% by mole, the refractive index cannot be reduced withoutlowering the Tg of the polyimide. At more than 90% by mole, anorganosiloxane group cannot be sufficiently introduced.

It is desirable that a repeating unit having an organosiloxane grouprepresented by the general formula (5) in a polyimide according to anembodiment of the present invention be 5% by mole or more and 50% bymole or less, preferably 10% by mole or more and 40% by mole or less, ofall the repeating units of the polyimide. Within these ranges, therefractive index and the optical dispersion of the polyimide can bemarkedly reduced, and the solubility of the polyimide in organicsolvents can be improved.

A method for forming a polyimide layer 2 according to an embodiment ofthe present invention will be described below.

In the formation of the polyimide layer 2 using a polyimide synthesizedas described above, a solution containing the synthesized polyimide isapplied to a substrate or a thin film formed on the substrate and isdried or fired at 100° C. or more and 250° C. or less.

A polyimide solution produced in the polyimide synthesis may be directlyused in the formation of the polyimide layer 2. Alternatively, thepolyimide solution may be poured into a poor solvent to precipitate apolyimide powder, which is filtered off, dried, and dissolved in asolvent again. In the latter case, reprecipitation in an alcohol canremove unreacted monomers and various chemicals used in the imidization.

Examples of the solvent in which the precipitated polyimide powder is tobe dissolved include, but are not limited to, ketones, such as2-butanone, methyl isobutyl ketone, cyclopentanone, and cyclohexanone;esters, such as ethyl acetate, n-butyl acetate, ethylene glycolmonomethyl ether acetate, propylene glycol monomethyl ether acetate,ethyl lactate, and γ-butyrolactone; ethers, such as tetrahydrofuran,dioxane, diisopropyl ether, dibutyl ether, cyclopentyl methyl ether, anddiglyme; aromatic hydrocarbons, such as toluene, xylene, andethylbenzene; chlorinated hydrocarbons, such as chloroform, methylenechloride, and tetrachloroethane; and others, such asN-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide,dimethyl sulfoxide, and sulfolane. Furthermore, alcohols, such as1-butanol, methyl cellosolve, and methoxypropanol may also be used.

It is desirable that the polyimide be soluble in organic solvents.

The polyimide solution can be applied by a known method, such asdipping, spin coating, spraying, printing, or flow coating, or acombination thereof.

The drying and/or firing of the polyimide solution is principallyperformed to remove the solvent. The polyimide solution can be heatedfor approximately five minutes to two hours. The polyimide solution maybe heated by light, radiation, or electromagnetic wave irradiation usinga circulating hot-air oven, a muffle furnace, infrared rays, or amicrowave.

It is desirable that the polyimide content of a polyimide layeraccording to an embodiment of the present invention be 70% by weight ormore, preferably 80% by weight or more and 100% by weight or less.

The polyimide layer 2 may contain a component other than the polyimideprovided that the component does not impair the optical properties,transparency, heat resistance, and water-fastness of the polyimide. Theamount of component other than the polyimide is less than 20 parts byweight per 100 parts by weight of the polyimide. Twenty parts by weightor more of the component other than the polyimide may impair thetransparency, the film strength, and the film thickness uniformity ofthe polyimide.

Examples of the component other than the polyimide include, but are notlimited to, silane coupling agents and phosphates for improvingadhesion; thermosetting resins, photocurable resins, and cross-linkers,such as epoxy resin, melamine resin, and acrylic resin, for improvingthe solvent resistance of the polyimide layer 2; and small amounts ofinorganic fine particles, such as SiO₂, TiO₂, ZrO₂, SiO₂, ZnO, MgO, andAl₂O₃, for controlling the refractive index or the film hardness of thepolyimide. It is desirable that the amount of component other than thepolyimide be 30% by weight or less, preferably 0% by weight or more and20% by weight or less.

The low-refractive index layer 3 formed on the polyimide layer 2 mayhave a refractive index of 1.4 or less and may be composed of a metaloxide, a metal halide, or a fluoropolymer. The low-refractive indexlayer 3 formed of a porous layer mainly composed of silicon oxide,magnesium fluoride, or a fluorinated acrylic polymer or a layer having afine textured structure mainly composed of silicon oxide, aluminumoxide, or a transparent polymer can have a higher antireflection effect.

An optical member according to an embodiment of the present inventionmay have a textured structure on the outermost surface of the laminatedbody. The textured structure may be formed of plate crystals mainlycomposed of aluminum oxide.

FIG. 2 is a schematic view of an optical member according to anotherembodiment of the present invention. In FIG. 2, the optical memberaccording to this embodiment of the present invention includes apolyimide layer 2 and a layer 4 having a fine textured structure, on asurface of a substrate 1 in this order. The outermost surface has a finetextured structure 5.

The fine textured structure 5 of the layer 4 having a fine texturedstructure in a laminated body 9 can be formed of plate crystals ofaluminum oxide. The plate crystals of aluminum oxide refer to platecrystals deposited and grown on a surface layer of a film mainlycomposed of aluminum oxide by immersing the film into hot water topeptize the surface layer.

As illustrated in FIG. 3, the refractive index of the layer 4 having afine textured structure may continuously increase from the top towardthe substrate in a linear (a) or curved (b or c) manner. The layer 4having a refractive index that continuously increases from the toptoward the substrate has a higher reflectance-reduction effect than aplurality of layers in which the refractive index increases layer bylayer from the top.

The fine textured structure is formed of crystals mainly composed of anoxide of aluminum, a hydrate of an oxide of aluminum, or a hydroxide ofaluminum. The textured structure is preferably formed of crystalscontaining 70% by mole or more, more preferably 90% by mole or more, ofan oxide of aluminum, a hydrate of an oxide of aluminum, or a hydroxideof aluminum. These crystals are herein referred to as plate crystals. Inparticular, the plate crystals can be formed of boehmite. Since thetextured structure 5 having fine ridges is formed of plate crystals, theplate crystals are disposed at a particular angle with respect to thesubstrate surface to increase the height and reduce the intervals of thefine ridges. An oxide of aluminum, a hydroxide of aluminum, and hydratesof these compounds are herein collectively referred to as aluminumoxide. One or more oxide layers formed of aluminum oxide alone or 70% bymole or more, preferably 90% by mole or more, of aluminum oxide andZrO₂, SiO₂, TiO₂, ZnO, or MgO are hereinafter referred to as a layermainly composed of aluminum oxide.

In FIG. 4, a substrate 1, such as a plate, a film, or a sheet, has aflat surface. It is desirable that plate crystals be disposed such thatthe average of the angles 81 between the slopes 6 of the plate crystalsand the substrate surface is 45° or more and 90° or less, preferably 60°or more and 90° or less.

In FIG. 5, a substrate 1 has a two-dimensionally or three-dimensionallycurved surface. It is desirable that plate crystals be disposed suchthat the average of the angles θ2 between the slopes 7 of the platecrystals and the tangent line 8 of the substrate surface is 45° or moreand 90° or less, preferably 60° or more and 90° or less. If the anglesθ1 and θ2 are more than 90°, their supplementary angles are consideredas the angles θ1 and θ2.

The thickness of the layer 4 having a fine textured structure ispreferably 20 nm or more and 1000 nm or less, more preferably 50 nm ormore and 1000 nm or less. The thickness of the layer 4 having a finetextured structure in the range of 20 to 1000 nm results in effectiveantireflection performance of the fine textured structure, eliminatesthe possibility of reduction in the mechanical strength of the fineridges, and provides advantages in the manufacturing costs of the finetextured structure. The thickness of the layer 4 having a fine texturedstructure in the range of 50 to 1000 nm can further improveantireflection performance.

The surface density of the fine ridges is also important and can berepresented by the average surface roughness Ra′ and the surface arearatio Sr, which is defined later. The average surface roughness Ra′ canbe determined by applying the measurement of center-line averageroughness to the surface. The average surface roughness Ra′ is 5 nm ormore, preferably 10 nm or more, more preferably 15 nm or more and 100 nmor less. The surface area ratio Sr is 1.1 or more, preferably 1.15 ormore, more preferably 1.2 or more and 3.5 or less.

One of methods for evaluating the fine textured structure is theobservation of the fine textured surface with a scanning probemicroscope. The average surface roughness Ra′ and the surface area ratioSr can be determined through this observation. As mentioned above, theaverage surface roughness Ra′ (nm) can be determined bythree-dimensionally applying the measurement of center-line averageroughness Ra defined in JIS B 0601 to a surface to be measured. Theaverage surface roughness Ra′ refers to “the average of the absolutevalues of deviations of specified planes from the reference plane” andis expressed by the following equation (1):

[Math.  1] $\begin{matrix}{{Ra}^{\prime} = {\frac{1}{S_{0}}{\int_{Y_{B}}^{Y_{T}}{\int_{X_{L}}^{X_{R}}{{{{F( {X,Y} )} - Z_{0}}}\ {_{X}\ _{Y}}}}}}} & (1)\end{matrix}$

wherein

Ra′: average surface roughness (nm);

S₀: the area of a surface to be measured, on the assumption that thesurface is flat, |XR−X_(L)|×|Y_(T)−Y_(B)|;

F(X,Y): a height at a point of measurement (X,Y), wherein X denotes thex-coordinate, and Y denotes the y-coordinate;

X_(L) to X_(R): the range of the surface to be measured on thex-coordinate;

Y_(B) to Y_(T): the range of the surface to be measured on they-coordinate; and

Z₀: the average height of the surface to be measured.

The surface area ratio Sr can be determined by Sr=S/S₀ wherein S₀denotes the area of a surface to be measured, on the assumption that thesurface is flat, and S denotes the actual surface area of the surface tobe measured. The actual surface area of the surface to be measured isdetermined as described below. First, the surface to be measured isdivided into minute triangles defined by adjacent three data points (A,B, and C). The area ΔS of each of the minute triangles is thendetermined utilizing a vector product.ΔS(ΔABC)=[s(s−AB)(s−BC)(s−AC)]0.5, wherein AB, BC, and AC denote thelengths of their respective sides. s≡0.5 (AB+BC+AC)]. The surface area Sis the sum total of ΔS's. When the surface density of the fine ridges issuch that Ra′ is 5 nm or more and Sr is 1.1 or more, the texturedstructure can exhibit antireflection. Ra′ of 10 nm or more and Sr of1.15 or more result in a higher antireflection effect. When Ra′ is 15 nmor more and Sr is 1.2 or more, the fine textured structure is actuallyuseful. When Ra′ is 100 nm or more and Sr is 3.5 or more, however,scattering due to the textured structure predominates over theantireflection effect, resulting in poor antireflection performance.

In the case that the layer 4 having a fine textured structure is mainlycomposed of aluminum oxide, a metal film made of metallic Al alone or ametal film made of metallic Al and metallic Zn or metallic Mg is formedon the polyimide layer 2. Immersion in hot water at 50° C. or more orexposure to water vapor forms the textured structure 5 on the metalsurface by hydration, dissolution, and reprecipitation. Likewise,hot-water immersion or water vapor exposure of a layer mainly composedof aluminum oxide formed on a layer 2 mainly composed of organic resincan also precipitate the fine textured structure 5 on the surface. Thelayer mainly composed of aluminum oxide can be formed by a known gasphase method, such as chemical vapor deposition (CVD) or physical vapordeposition (PVD), a known liquid phase method, such as a sol-gel method,or a known hydrothermal synthesis using an inorganic salt. In such amethod involving the formation of plate crystals of aluminum oxide, anamorphous aluminum oxide layer may remain under the textured structure 5in the layer 4 having a fine textured structure.

A gel film formed by the application of a sol-gel coating liquidcontaining aluminum oxide can be treated with hot water to grow aluminaplate crystals. This method can form a uniform antireflection layer on alarge-area or nonplanar substrate.

The raw material of the gel film formed by the application of a sol-gelcoating liquid containing aluminum oxide contains an Al compound aloneor an Al compound and at least one compound selected from Zr, Si, Ti,Zn, and Mg compounds. Metal alkoxides and salt compounds, such aschlorides and nitrates, may be used as the raw materials for Al₂O₃,ZrO₂, SiO₂, TiO₂, ZnO, and MgO. In particular, metal alkoxides may beused as ZrO₂, SiO₂, and TiO₂ raw materials because of their excellentfilm-forming properties.

Examples of the aluminum compound include, but are not limited to,aluminum ethoxide, aluminum isopropoxide, aluminum-n-butoxide,aluminum-sec-butoxide, aluminum-tert-butoxide, and aluminumacetylacetonate, oligomers thereof, aluminum nitrate, aluminum chloride,aluminum acetate, aluminum phosphate, aluminum sulfate, and aluminumhydroxide.

Specific examples of the zirconium alkoxide include, but are not limitedto, zirconium tetramethoxide, zirconium tetraethoxide, zirconiumtetra-n-propoxide, zirconium tetraisopropoxide, zirconiumtetra-n-butoxide, and zirconium tetra-t-butoxide.

The silicon alkoxide may be represented by the general formula Si(OR)₄.R's may be the same or different lower alkyl groups, such as a methylgroup, an ethyl group, a propyl group, an isopropyl group, a butylgroup, and an isobutyl group.

Examples of the titanium alkoxide include, but are not limited to,tetramethoxytitanium, tetraethoxytitanium, tetra-n-propoxytitanium,tetraisopropoxytitanium, tetra-n-butoxytitanium, andtetraisobutoxytitanium.

Examples of the zinc compound include, but are not limited to, zincacetate, zinc chloride, zinc nitrate, zinc stearate, zinc oleate, andzinc salicylate, particularly zinc acetate and zinc chloride.

Examples of the magnesium compound include, but are not limited to,magnesium alkoxides, such as dimethoxymagnesium, diethoxymagnesium,dipropoxymagnesium, and dibutoxymagnesium, magnesium acetylacetonate,and magnesium chloride.

The organic solvent may be any organic solvent that does not induce thegelation of the raw materials described above, such as alkoxides.Examples of the organic solvent include, but are not limited to,alcohols, such as methanol, ethanol, 2-propanol, butanol, pentanol,ethylene glycol, and ethylene glycol-mono-n-propyl ether; aliphatic oralicyclic hydrocarbons, such as n-hexane, n-octane, cyclohexane,cyclopentane, and cyclooctane; aromatic hydrocarbons, such as toluene,xylene, and ethylbenzene; esters, such as ethyl formate, ethyl acetate,n-butyl acetate, ethylene glycol monomethyl ether acetate, ethyleneglycol monoethyl ether acetate, and ethylene glycol monobutyl etheracetate; ketones, such as acetone, methyl ethyl ketone, methyl isobutylketone, and cyclohexanone; ethers, such as dimethoxyethane,tetrahydrofuran, dioxane, and diisopropyl ether; chlorinatedhydrocarbons, such as chloroform, methylene chloride, carbontetrachloride, and tetrachloroethane; and aprotic polar solvents, suchas N-methylpyrrolidone, dimethylformamide, dimethylacetamide, andethylene carbonate. Among the solvents described above, alcohols canprovide particularly excellent solution stability.

Among the alkoxide raw materials, aluminum, zirconium, and titaniumalkoxides have particularly high reactivity to water and are abruptlyhydrolyzed by the action of moisture in the air or the addition ofwater, producing turbidity and precipitation in the solution. Aluminumsalt compounds, zinc salt compounds, and magnesium salt compounds aredifficult to dissolve in organic solvents and provide low solutionstability. To avoid these problems, a stabilizer may be added tostabilize the solution.

Examples of the stabilizer include, but are not limited to, β-diketonecompounds, such as acetylacetone, dipivaloylmethane,trifluoroacetylacetone, hexafluoroacetylacetone, benzoylacetone, anddibenzoylmethane; β-ketoester compounds, such as methyl acetoacetate,ethyl acetoacetate, allyl acetoacetate, benzyl acetoacetate, iso-propylacetoacetate, tert-butyl acetoacetate, iso-butyl acetoacetate,2-methoxyethyl acetoacetate, and 3-keto-methyl-n-valerate; andalkanolamines, such as monoethanolamine, diethanolamine, andtriethanolamine. The molar ratio of the stabilizer to alkoxide or a saltcompound can be approximately one. After the addition of the stabilizer,a catalyst can be added to promote part of reactions to form a desiredprecursor. Examples of the catalyst include, but are not limited to,nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, aceticacid, and ammonia. Examples of a method for applying the sol-gel coatingliquid to form a film include, but are not limited to, known methods,such as dipping, spin coating, spraying, printing, and flow coating, andcombinations of these methods.

The application of the sol-gel coating liquid is preferably followed byheat treatment at 100° C. or more and 230° C. or less, more preferably120° C. or more and 200° C. or less. Although a higher heat-treatmenttemperature results in a greater density of the film, a heat-treatmenttemperature higher than 230° C. may cause damage, such as deformation,to the substrate. The heating time depends on the heating temperatureand may be 10 minutes or more.

The gel film after drying or heat-treatment is immersed in hot water toprecipitate plate crystals mainly composed of aluminum oxide, formingfine ridges on the outermost surface. Immersion in hot water peptizesthe surface layer of the gel film containing aluminum oxide and elutespart of the components of the gel film. Owing to difference in hot-watersolubility between hydroxides, plate crystals mainly composed ofaluminum oxide are deposited and grown on the surface layer of the gelfilm. The temperature of hot water can range from 40° C. to 100° C. Thehot-water treatment time may range from approximately 5 minutes to 24hours.

In the hot-water treatment of a gel film containing aluminum oxide asthe main component and an oxide, such as TiO₂, ZrO₂, SiO₂, ZnO, or MgO,as a different component, crystallization is related to difference inhot-water solubility between the components. Unlike the hot-watertreatment of a film formed of aluminum oxide alone, therefore, theratios of the inorganic components can be altered to control the size ofplate crystals. This allows the shape of fine ridges formed of the platecrystals to be widely controlled within the range described above. Useof ZnO as an accessory component allows eutectic crystallization withaluminum oxide. This allows further wide control of refractive index,thereby achieving excellent antireflection performance.

Examples of the material of the substrate 1 include, but are not limitedto, glass, resin, glass mirrors, and resin mirrors. Representativeexamples of the resin substrate include, but are not limited to, filmsand formed products made of thermoplastic resins, such as polyester,cellulose triacetate, cellulose acetate, poly(ethylene terephthalate),polypropylene, polystyrene, polycarbonate, polysulfone, polyacrylate,polymethacrylate, ABS resin, poly(phenylene oxide), polyurethane,polyethylene, polycycloolefin, and poly(vinyl chloride); andcross-linked films and cross-linked formed products made of variousthermosetting resins, such as unsaturated polyester resin, phenolicresin, cross-linking polyurethane, cross-linking acrylic resin, andcross-linking saturated polyester resin. Specific examples of the glassinclude, but are not limited to, non-alkali glass and aluminosilicateglass. A substrate for use in the present invention may be anysubstrate, such as a plate, a film, or a sheet, that can have a shapefor each intended use and may be a substrate having a two- orthree-dimensionally curved surface. The thickness of the substrate isgenerally, but is not limited to, 5 mm or less.

An optical transparent member according to an embodiment of the presentinvention may further include another functional layer. For example, ahard coat layer may be disposed on the layer having a fine texturedstructure to improve the film hardness. A water repellent layer, forexample, formed of fluoroalkylsilane or alkylsilane may be formed toprevent the adhesion of dirt. An adhesive layer or a primer layer may beformed to improve the adhesion between the substrate and the polyimidelayer.

EXAMPLES

The present invention will be further described in the followingexamples. However, the present invention is not limited to theseexamples. Optical films having fine ridges prepared in examples andcomparative examples were evaluated as described below.

(1) Purification of 4,4′-methylenebis(aminocyclohexane)

Hexane was gradually added under reflux to 200 g of4,4′-methylenebis(aminocyclohexane) (hereinafter referred to as DADCM,manufactured by Tokyo Chemical Industry Co., Ltd.).4,4′-methylenebis(aminocyclohexane) was completely dissolved in hexane.After heating was completed, the solution was left to stand for several(two to four) days at room temperature (20° C. to 25° C.). A precipitatewas filtered off and dried under vacuum to yield 61 g of white purifiedDADCM in a solid state. ¹H-NMR spectrum showed that the DADCM contained95% by mole of trans-1,4-cyclohexylene group.

¹H-NMR (DMSO-d₆); δ0.83 (2H, m), δ0.97 (2H, q), δ1.18 (2H, m), δ1.60(2H, d), δ1.69 (2H, d), δ2.05 (2H, s), δ2.42 (2H, m), δ3.30 (4H, b)

(2) Synthesis of Polyimides 1 to 8

A total of 0.012 mol of diamine (1) (purified DADCM or crude DADCM),diamine (2), and diamine (3) were dissolved in N,N-dimethylacetamide(hereinafter referred to as DMAc). 0.012 mol of acid dianhydride wasadded to the diamine solution while the diamine solution was cooled withwater. DMAc was used in such an amount that the total mass of thediamines and the acid dianhydride was 20% by weight.

This solution was stirred at room temperature for 15 hours to causepolymerization reaction. After the solution was diluted with DMAc to 8%by weight, 7.4 ml of pyridine and 3.8 ml of acetic anhydride were added.The solution was stirred at room temperature for one hour. The solutionwas stirred in an oil bath at a temperature in the range of 60° C. to70° C. for four hours. The polymerization solution was poured intomethanol or a methanol/water mixed solvent for reprecipitation. Apolymer thus reprecipitated was removed and was washed several times inmethanol or a methanol/water mixed solvent. The polymer was dried undervacuum at 100° C. to yield a white to light yellow polyimide powder. Theimidization rate was determined by measuring the residual amount ofcarboxy group from a ¹H-NMR spectrum. Table 1 shows the compositions ofpolyimides 1 to 8.

TABLE 1 Trans-1,4- cyclohexylene Acid content Imidization Polyimidedianhydride Diamine (1) (% by mole) Diamine (2) Diamine (3) Yield % rate% Polyimide 1 TDA(1.0) Purified 95 PAM-E(0.1) — 92 96 DADCM(0.9)Polyimide 2 TDA(1.0) Crude 47 PAM-E(0.1) — 90 95 DADCM(0.9) Polyimide 3TDA(1.0) Purified 95 BAPB(0.3) PAM-E(0.1) 94 98 DADCM(0.6) Polyimide 4TDA(1.0) Crude 47 BAPB(0.3) PAM-E(0.1) 93 98 DADCM(0.6) Polyimide 5BDA(1.0) Purified 95 PAM-E(0.1) — 85 95 DADCM(0.9) Polyimide 6 BDA(1.0)Crude 47 PAM-E(0.1) — 81 95 DADCM(0.9) Polyimide 7 6FDA(1.0) Purified 95PAM-E(0.1) -— 89 96 DADCM(0.9) Polyimide 8 6FDA(1.0) Crude 47 PAM-E(0.1)— 89 95 DADCM(0.9)

(Note 1)

TDA:4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylicanhydride

BDA: meso-butane-1,2,3,4-tetracarboxylic acid dianhydride

DADCM: 4,4′-methylenebis(aminocyclohexane)

PAM-E: dimethylsiloxane oligomer in which both ends were modified withamine

BAPB: 4,4′-bis(4-aminophenoxy)biphenyl

6FDA: 4,4′-(hexafluoroisopropylidene)diphthalic acid anhydride

(Note 2)

Values in parentheses for acid dianhydride and diamines represent themolar ratio of these compounds charged.

(Note 3)

The trans-1,4-cyclohexylene group in the purified4,4′-methylenebis(aminocyclohexane) accounted for 95% by mole of the1,4-cyclohexylene group in the purified4,4′-methylenebis(aminocyclohexane).

(3) Preparation of Polyimide Solutions 1 to 9 and 11 to 13

2.0 to 4.0 g of a powder of each of the polyimides 1 to 8 was dissolvedin 96 to 98 g of a cyclopentanone/cyclohexanone mixed solvent to preparepolyimide solutions 1 to 9 and 11 to 13.

(4) Preparation of Polyimide Solutions 10 and 14

2.0 g of a powder of polyimide 1 or 2 and 0.3 g of melamine resin (tradename: Nikalac MX-706, manufactured by Nippon Carbide Industries Co.,Inc.) were dissolved in 997 g of a cyclopentanone/cyclohexanone mixedsolvent to prepare polyimide solutions 10 and 14. Table 2 shows thepolyimide solutions prepared.

TABLE 2 Cross- Solid Polyimide solution Polyimide linker content %Polyimide solution 1 Polyimide 1 — 2% Polyimide solution 2 Polyimide 1 —3% Polyimide solution 3 Polyimide 1 — 4% Polyimide solution 4 Polyimide2 — 2% Polyimide solution 5 Polyimide 2 — 3% Polyimide solution 6Polyimide 2 — 4% Polyimide solution 7 Polyimide 3 — 2% Polyimidesolution 8 Polyimide 5 — 2% Polyimide solution 9 Polyimide 7 — 2%Polyimide solution 10 Polyimide 1 MX-706 2% Polyimide solution 11Polyimide 4 — 2% Polyimide solution 12 Polyimide 6 — 2% Polyimidesolution 13 Polyimide 8 — 2% Polyimide solution 14 Polyimide 2 MX-706 2%

(5) Preparation of Aluminum Oxide (Alumina (Al₂O₃)) Sol

22.2 g of Al(O-sec-Bu)₃, 5.86 g of ethyl 3-oxobutanate, and4-methyl-2-pentanol were stirred until the mixture became homogeneous.1.62 g of 0.01 M diluted hydrochloric acid dissolved in a4-methyl-2-pentanol/1-ethoxy-2-propanol mixed solvent was graduallyadded to the Al(O-sec-Bu)₃ solution and was stirred for a short time.The solvent was finally adjusted so as to contain 49.3 g of4-methyl-2-pentanol and 21.1 g of 1-ethoxy-2-propanol. The solution wasstirred in an oil bath at 120° C. for another three hours or more toprepare a precursor sol of aluminum oxide.

(6) Cleaning of Substrate

Various glass substrates having a diameter of approximately 30 mm and athickness of approximately 2 mm, both surfaces of each of which werepolished, were ultrasonically cleaned with an alkaline detergent andisopropyl alcohol (IPA) and were dried in an oven.

(7) Measurement of Reflectance

Reflectance was measured with an absolute reflectometer (USPM-RU,manufactured by Olympus Co.) at a wavelength in the range of 400 to 700nm at an incident angle of 0°.

(8) Measurement of Film Thickness and Refractive Index

The film thickness and the refractive index were measured with aspectroscopic ellipsometer (VASE, manufactured by J. A. Woollam JapanCo., Inc.) at a wavelength in the range of 380 to 800 nm.

(9) Observation of Substrate Surface

A substrate surface treated with Pd/Pt was observed with a fieldemission scanning electron microscope (FE-SEM) (S-4800, manufactured byHitachi High-Technologies Co.) at an accelerating voltage of 2 kV.

Example 1

A polished and cleaned surface of glass A mainly composed of La₂O₅ andhaving an nd of 1.77 and a νd of 50 was spin-coated with a proper amountof polyimide solution 1, 2, or 3 at 3000 to 4000 rpm. The substrate wasdried at 200° C. for 60 minutes to form a film made of the polyimide 1synthesized from purified DADCM on the substrate.

The thickness and the refractive index of the film of the polyimide 1were measured by ellipsometry. After the film of the polyimide 1 wasimmersed in hot water at 80° C. for 20 minutes, the thickness and therefractive index of the film were measured again. FIG. 6 shows the rateof increase in film thickness due to the immersion in hot water as afunction of the initial film thickness. The rate of increase in filmthickness due to the hot-water treatment of the film having an initialthickness of 100 nm or more ranged from 0.32% to 0.34%. The rate ofincrease in film thickness due to the hot-water treatment of the filmhaving an initial thickness in the range of 40 to 50 nm ranged from 0.6%to 0.69%.

Comparative Example 1

The same procedures as Example 1 were performed except that thepolyimide solutions 1, 2, and 3 were replaced with the polyimidesolutions 4, 5, and 6 and that a layer was formed of the polyimide 2synthesized from crude DADCM.

FIG. 6 shows the rate of increase in film thickness due to immersion inhot water as a function of the initial film thickness. The rate ofincrease in film thickness due to the hot-water treatment of the filmhaving an initial thickness of 100 nm or more ranged from 0.36% to 0.4%.The rate of increase in film thickness due to the hot-water treatment ofthe film having an initial thickness in the range of 40 to 50 nm rangedfrom 0.74% to 0.93%. Thus, the rate of increase in film thickness due tomoisture absorption during the hot-water treatment was higher than thatof the film of the polyimide 1.

Examples 2 to 5

A polished and cleaned surface of glass A mainly composed of La₂O₅ andhaving an nd of 1.77 and a νd of 50 was spin-coated with a proper amountof polyimide solution 7, 8, 9, or 10 at 3000 to 4000 rpm. The substratewas dried at 200° C. for 60 minutes to form a film made of the polyimide3, 5, or 7 synthesized from purified DADCM or a film made of thepolyimide 1 and a cross-linker on the substrate.

The thickness and the refractive index of each of the polyimide filmswere measured by ellipsometry. After the polyimide films were immersedin hot water at 80° C. for 20 minutes, the thickness and the refractiveindex of each of the films were measured again. Table 3 shows the rateof increase in film thickness due to the immersion in hot water relativeto the initial film thickness.

Comparative Examples 2 to 5

The same procedures as Examples 2 to 5 were performed except that thepolyimide solutions 7 to 10 were replaced with the polyimide solutions11 to 14 and that a film was formed of the polyimide 4, 6, or 8synthesized from crude DADCM or the polyimide 2 and a cross-linker.

Table 3 shows the rate of increase in film thickness due to immersion inhot water relative to the initial film thickness. The rates of increasein film thickness due to hot-water treatment were higher than those ofExamples 2 to 5.

TABLE 3 Rate of increase in Film Refractive film thickness due Cross-thickness index to hot water Polyimide linker (nm) (550 nm) treatment %Example 1 Polyimide 1 — 42 1.56 0.68 Example 2 Polyimide 3 — 43 1.600.50 Example 3 Polyimide 5 — 43 1.53 0.75 Example 4 Polyimide 7 — 431.55 0.55 Example 5 Polyimide 1 MX-706 44 1.56 0.57 ComparativePolyimide 2 — 44 1.56 0.93 example 1 Comparative Polyimide 4 — 42 1.600.81 example 2 Comparative Polyimide 6 — 41 1.53 1.01 example 3Comparative Polyimide 8 — 40 1.55 0.85 example 4 Comparative Polyimide 2MX-706 46 1.56 0.84 example 5

Examples 6 and 7

A polished and cleaned surface of glass A mainly composed of La₂O₅ andhaving an nd of 1.77 and a νd of 50 was spin-coated with a proper amountof polyimide solution 1 or 7 at 3000 to 4000 rpm. The substrate wasdried at 200° C. for 60 minutes to form a film made of the polyimide 1or 3 synthesized from purified DADCM on the substrate. The thickness andthe refractive index of each of the polyimide films were measured byellipsometry. After the polyimide films were left to stand at 60° C. and90% RH for 250 hours, the thickness and the refractive index of each ofthe films were measured again. Table 4 shows the rate of increase infilm thickness due to high temperature and high humidity relative to theinitial film thickness.

Comparative Examples 6 and 7

The same procedures as Examples 6 and 7 were performed except that thepolyimide solutions 1 and 7 were replaced with the polyimide solutions 4and 11 and that a layer was formed of the polyimide 2 or 4 synthesizedfrom crude DADCM.

Table 4 shows the rate of increase in film thickness due to hightemperature and high humidity relative to the initial film thickness.The rates of increase in film thickness due to high temperature and highhumidity were higher than those of Examples 6 and 7.

TABLE 4 Rate of increase in Film Refractive film thickness due Cross-thickness index to hot water Polyimide linker (nm) (550 nm) treatment %Example 6 Polyimide 1 — 43 1.56 2.60 Example 7 Polyimide 3 — 43 1.602.65 Comparative Polyimide 2 — 43 1.56 3.42 example 6 ComparativePolyimide 4 — 42 1.60 3.39 example 7

Example 8

A polished and cleaned surface of glass A mainly composed of La₂O₅ andhaving an nd of 1.77 and a νd of 50 was spin-coated with a proper amountof polyimide solution 1 at 3000 to 4000 rpm. The substrate was dried at200° C. for 60 minutes to form a film made of the polyimide 1synthesized from purified DADCM on the substrate.

The substrate on which the film of the polyimide 1 was formed wasspin-coated with a proper amount of precursor sol of aluminum oxide at4000 rpm for 20 seconds and was fired in a circulating hot-air oven at200° C. for 120 minutes. Thus, the film of the polyimide 1 was coatedwith an amorphous aluminum oxide film. The substrate was then immersedin hot water at 80° C. for 20 minutes and was dried at 60° C. for 15minutes.

The FE-SEM observation of the film surface showed the presence of fineridges formed of random complicated plate crystals mainly composed ofaluminum oxide.

Table 5 shows the absolute reflectance of the optical film on the glassA. The resulting antireflection-coated glass substrate had an absolutereflectance of 0.2% or less at a wavelength in the range of 450 to 650nm. There was no detachment and crack observed.

Example 9

The same procedures as Example 8 were performed except that the glass Awas replaced with glass B mainly composed of TiO₂ and having an nd of1.78 and a νd of 26.

The absolute reflectance of the optical film on the glass B wasmeasured. The resulting antireflection-coated glass substrate had anabsolute reflectance of 0.2% or less at a wavelength in the range of 450to 650 nm. There was no detachment and crack observed.

Comparative Example 8

The same procedures as Example 8 were performed except that thepolyimide solutions 1 was replaced with the polyimide solution 4 andthat a layer was formed of the polyimide 2 synthesized from crude DADCM.

Although there was no detachment and crack observed, the absolutereflectance of an optical film on glass A at a wavelength in the rangeof 450 to 650 nm varied between 0.2% and 0.3%.

Comparative Example 9

The same procedures as Example 9 were performed except that thepolyimide solution 1 was replaced with the polyimide solution 4 and thata layer was formed of the polyimide 2 synthesized from crude DADCM.

The absolute reflectance of an optical film on glass B at a wavelengthin the range of 450 to 650 nm varied between 0.2% and 0.3%. Furthermore,cracking was observed in a surrounding area.

TABLE 5 Absolute reflectance Obser- Cross- (450~ vation SubstratePolyimide linker 550 nm) on film Example 8 Glass A Polyimide 1 —   <0.2%Good (nd = 1.77) Example 9 Glass B Polyimide 1 —   <0.2% Good (nd =1.78) Comparative Glass A Polyimide 2 — 0.2~0.3% Uneven example 8 (nd =1.77) color Comparative Glass B Polyimide 2 — 0.2~0.3% Crack example 9(nd = 1.78)

Examples in which the solubility and the glass transition temperature ofpolyimides were measured will be described below.

(10) Purification of 4,4′-methylenebis(aminocyclohexane)

Hexane was gradually added under reflux to 200 g of4,4′-methylenebis(aminocyclohexane) (hereinafter referred to as DADCM,manufactured by Tokyo Chemical Industry Co., Ltd.).4,4′-methylenebis(aminocyclohexane) was completely dissolved in hexane.After heating was completed, the solution was left to stand in arefrigerator for several days. A precipitate was filtered off and driedunder vacuum to yield 61 g of white purified DADCM in a solid state.

¹H-NMR (DMSO-d₆); δ0.83 (2H, m), δ0.97 (2H, q), δ1.18 (2H, m), δ1.60(2H, d), δ1.69 (2H, d), δ2.05 (2H, s), δ2.42 (2H, m), δ3.30 (4H, b)

(11) DSC Measurement of 4,4′-methylenebis(aminocyclohexane)

The melting points of crude DADCM and purified DADCM were measured witha differential scanning calorimeter (hereinafter referred to as a DSC,manufactured by Seiko Instruments Inc., trade name DSC 200) at a heatingrate of 10° C./min. FIG. 7 shows the results. ΔQ denotes the amount ofheat, Exo. denotes exothermic, and Endo. denotes endothermic.

(12) Gas Chromatography of 4,4′-methylenebis(aminocyclohexane)

The isomer contents of crude DADCM and purified DADCM were measured witha GC/MS system (manufactured by Agilent Technologies, trade name 6890Nnetwork GC) equipped with a GC column (manufactured by AgilentTechnologies, trade name HP-35). Peaks assigned to a trans-trans isomer,a trans-cis isomer, and a cis-cis isomer were observed in ascendingorder of retention time. From the areas of these peaks, the transcontent (% by mole) of the 1,4-cyclohexylene group was calculated by thefollowing equation: Trans content=([trans-trans isomer peakarea]+[trans-cis isomer peak area]/2)/[total peak area of threeisomers].

(13) Synthesis of Polyimides 9 to 22

A total of 0.012 mol of diamine (1) (purified DADCM or crude DADCM),diamine (2), and diamine (3) (organosiloxane diamine) were dissolved inN,N-dimethylacetamide (hereinafter referred to as DMAc). 0.012 mol ofacid dianhydride was added to the diamine solution while the diaminesolution was cooled with water. DMAc was used in such an amount that thetotal mass of the diamines and the acid dianhydride was 20% by weight.

This solution was stirred at room temperature for 15 hours to causepolymerization reaction. After the solution was diluted with DMAc to 8%by weight, 7.4 ml of pyridine and 3.8 ml of acetic anhydride were added.The solution was stirred at room temperature for one hour. The solutionwas stirred in an oil bath at a temperature in the range of 60° C. to70° C. for four hours. The polymerization solution was poured intomethanol or a methanol/water mixed solvent for reprecipitation. Apolymer thus reprecipitated was removed and was washed several times inmethanol or a methanol/water mixed solvent. The polymer was dried undervacuum at 100° C. to yield a white to light yellow polyimide powder. Theimidization rate was determined by measuring the residual amount ofcarboxy group from a ¹H-NMR spectrum.

(14) Evaluation of Solubility

1.0 g of a powder of each of the polyimides 9 to 22 was added to 4 geach of five solvents: N,N-dimethylacetamide (hereinafter referred to asDMAc), N-methyl-2-pyrrolidone (hereinafter referred to as NMP),γ-butyrolactone, cyclopentanone, and cyclohexanone to examinesolubility. Table 7 shows the results, in which “Good” indicates solubleat room temperature, “Fair” indicates soluble by heating, and “Poor”indicates insoluble even by heating.

(15) Measurement of Glass Transition Temperature (Tg) of Polyimide

An aluminum pan filled with a polyimide powder was heated in the DSCfrom room temperature to 300° C. at 20° C./min to measure the glasstransition temperature of the polyimide. Table 8 shows the results.

(16) Measurement of Refractive Index

A polished surface of glass A having an nd of 1.77 and a νd of 50 wasspin-coated at 3000 to 4000 rpm with a proper amount of solution inwhich 4.0 g of a powder of each of the polyimides 9 to 22 was dissolvedin 96 g of a cyclopentanone/cyclohexanone mixed solvent. The substratewas dried at 200° C. for 60 minutes to form a film of each of thepolyimides 9 to 22 having a thickness of approximately 100 nm.

The refractive index of the polyimide film on the substrate was measuredwith a spectroscopic ellipsometer (VASE, manufactured by J. A. WoollamJapan Co., Inc.) at a wavelength in the range of 400 to 700 nm. Table 7shows the refractive index (550 nm) and Abbe number (νd) obtained fromthe refractive index.

Examples 10 to 16

As shown in Table 6, the polyimides 9 to 15 were synthesized by themethod described above using purified DADCM.

TABLE 6 Acid Trans-1,4-cyclohexylene Imidization Powder ExamplePolyimide dianhydride Diamine (1) content (% by mole) Diamine (2)Diamine (3) Yield % rate % properties Example 10 Polyimide 9  TDA(1.0)Purified 97 PAM-E(0.1) 92 96 White powder DADCM(0.9) Example 11Polyimide 10 TDA(1.0) Purified 97 BAPB(0.3) PAM-E(0.1) 94 98 Whitepowder DADCM(0.6) Example 12 Polyimide 11 BDA(1.0) Purified 97PAM-E(0.1) 85 95 White powder DADCM(0.9) Example 13 Polyimide 12BDA(1.0) Purified 97 PAM-E(0.2) 87 96 White powder DADCM(0.8) Example 14Polyimide 13 B4400(1.0) Purified 97 PAM-E(0.1) 85 95 Light yellowDADCM(0.9) powder Example 15 Polyimide 14 6FDA(1.0) Purified 97PAM-E(0.1) 89 96 White powder DADCM(0.9) Example 16 Polyimide 15DSDA(1.0) Purified 97 PAM-E(0.1) 84 97 Light yellow DADCM(0.9) powderComparative Polyimide 16 TDA(1.0) Crude 70 PAM-E(0.1) 90 95 Light yellowexample 10 DADCM(0.9) powder Comparative Polyimide 17 TDA(1.0) Crude 70BAPB(0.3) PAM-E(0.1) 93 98 Light yellow example 11 DADCM(0.6) powderComparative Polyimide 18 BDA(1.0) Crude 70 PAM-E(0.1) 81 95 Yellowpowder example 12 DADCM(0.9) (sticky) Comparative Polyimide 19 BDA(1.0)Crude 70 PAM-E(0.2) 85 95 Yellow powder example 13 DADCM(0.8) (sticky)Comparative Polyimide 20 B4400(1.0) Crude 70 PAM-E(0.1) 84 96 Yellowpowder example 14 DADCM(0.9) (sticky) Comparative Polyimide 21 6FDA(1.0)Crude 70 PAM-E(0.1) 89 95 Yellow powder example 15 DADCM(0.9) (sticky)Comparative Polyimide 22 DSDA(1.0) Crude 70 PAM-E(0.1) 79 97 Yellowpowder example 16 DADCM(0.9) (Note 1) TDA:4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylicanhydride BDA: meso-butane-1,2,3,4-tetracarboxylic acid dianhydrideDADCM: 4,4′-methylenebis(aminocyclohexane) PAM-E: dimethylsiloxaneoligomer in which both ends were modified with amine BAPB:4,4′-bis(4-aminophenoxy)biphenyl B4400:5-(2,5-dioxotetrahydrofury1)-3-methy1-3-cyclohexene-1,2-dicarboxylicanhydride 6FDA: 4,4′-(hexafluoroisopropylidene)diphthalic acid anhydrideDSDA: 3,3′,4,4′-diphenylsulfonetetracarboxylic acid dianhydride (Note 2)Values in parentheses for acid dianhydride and diamines represent themolar ratio of these compounds charged. (Note 3) The trans content (% bymole) represents the mole percentage of the trans-1,4-cyclohexylenegroup in the diamine 1 (DADCM).

The purified DADCM used as a monomer was obtained by recrystallizationof commercial DADCM. ¹H-NMR spectrum and gas chromatography provedalmost complete isolation of a trans-trans structural isomer. Table 6shows the trans content measured by gas chromatography before and afterpurification. As illustrated in FIG. 7, the DSC measurement of purifiedDADCM also showed one endothermic peak at a temperature in the range ofapproximately 70° C. to 71° C. probably assigned to the melting of thetrans-trans structural isomer.

The polyimides 9 to 15 synthesized were white to light yellow powdersand were soluble in DMAc and NMP at room temperature and soluble incyclopentanone, if necessary, by heating. Table 7 shows the results.

TABLE 7 Solubility Example Polyimide DMAc NMP γ-butyrolactoneCyclopentanone Cyclohexanone Example 10 Polyimide 9  Good Good Good GoodGood Example 11 Polyimide 10 Good Good Good Good Fair Example 12Polyimide 11 Good Good Poor Fair Fair Example 13 Polyimide 12 Good GoodGood Good Good Example 14 Polyimide 13 Good Good Good Good Good Example15 Polyimide 14 Good Good Poor Good Fair Example 16 Polyimide 15 GoodGood Poor Good Fair Comparative Polyimide 16 Good Good Good Good Goodexample 10 Comparative Polyimide 17 Good Good Good Good Good example 11Comparative Polyimide 18 Good Good Fair Fair Fair example 12 ComparativePolyimide 19 Good Good Good Good Good example 13 Comparative Polyimide20 Good Good Good Good Good example 14 Comparative Polyimide 21 GoodGood Fair Good Good example 15 Comparative Polyimide 22 Good Good PoorGood Fair example 16 (Note 1) DMAc: N,N-dimethylacetamide NMP:N-methyl-2-pyrrolidone

The DSC measurement of the polyimide clearly showed the presence of Tg.A polyimide produced using 0.1 molar equivalent of the organosiloxanediamine (PAM-E) had a Tg as high as 200° C. or more, which wascomparable to the Tg of a polyimide produced by copolymerization with anaromatic diamine (BAPB). A polyimide produced using 0.2 molar equivalentof PAM-E had a Tg as high as 190° C.

The refractive index measurement showed that some of the polyimides hada low refractive index below 1.55 and a high Abbe number in the range of27 to 45. The isolation of the trans form did not cause a change inrefractive index or an increase in Abbe number. Table 8 shows theresults.

TABLE 8 Refractive Comparative Refractive Example Polyimide Tg/° C.index vd example Polyimide Tg/° C. index vd Example 10 Polyimide 9  2281.565 38 Comparative Polyimide 16 212 1.564 37 example 10 Example 11Polyimide 10 227 1.61 28 Comparative Polyimide 17 215 1.610 28 example11 Example 12 Polyimide 11 211 1.538 43 Comparative Polyimide 18 1991.539 43 example 12 Example 13 Polyimide 12 190 1.525 45 ComparativePolyimide 19 150-170* 1.525 45 example 13 Example 14 Polyimide 13 2261.542 40 Comparative Polyimide 20 180-210* 1.541 40 example 14 Example15 Polyimide 14 220 1.557 27 Comparative Polyimide 21 180-200* 1.557 28example 15 Example 16 Polyimide 15 230 1.601 27 Comparative Polyimide 22218 1.600 27 example 16 (Note 1) *No distinct Tg was observed.

Comparative Examples 10 to 16

The same procedures as Examples 10 to 16 were performed except thatpolyimides 16 to 22 were synthesized using crude DADCM.

DSC measurement showed that crude DADCM had three broad endothermicpeaks probably assigned to the melting of cis-cis, cis-trans, andtrans-trans structural isomers.

The polyimides 9 to 15 synthesized in Examples 10 to 16 were white orlight yellow powders, whereas the polyimides 16 to 22 synthesized inComparative Examples 10 to 16 were light yellow or yellow polyimides. Inparticular, the polyimides 18 to 21 were yellow sticky polyimidepowders. Although the polyimides 16 to 22 had solubility inγ-butyrolactone substantially equivalent to or higher than thesolubility of the polyimides 9 to 15, the polyimides 16 to 22 had a 12°C. or more lower Tg than the polyimides 9 to 15. In particular, thepolyimides 19 to 21 had broad and indistinct Tg's.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

INDUSTRIAL APPLICABILITY

Optical members according to embodiments of the present invention can beapplied to transparent substrates having any refractive index, have anexcellent antireflection effect on visible light, and excellentlong-term weatherability. Thus, optical members according to embodimentsof the present invention can be used in various displays for use in wordprocessors, computers, television sets, plasma display panels, and thelike; optical members, such as polarizers for liquid crystal displays,and sunglass lenses, prescription glass lenses, viewing lens forcameras, prisms, fly-eye lenses, toric lenses, various optical filters,and sensors made of various optical lens materials and transparentplastics; imaging optical systems, optical systems for observation, suchas binoculars, and projection optical systems for use in liquid crystalprojectors, using these optical members; various optical lenses, such asscanning optical systems, for use in laser-beam printers; and opticalmembers, such as covers for various measuring instruments andwindowpanes for automobiles and trains.

1. A method for manufacturing an optical member including a laminatedbody that can reduce the reflection of light formed on a substratesurface, comprising: 1) purifying a diamine represented by the followinggeneral formula (3) such that a 1,4-cyclohexylene group in the mainchain of R₂ in the general formula (3) contains 90% by mole or more of atrans-1,4-cyclohexylene group;[Chem. 2]H₂N—R₂—NH₂  (3) wherein R₂ denotes a divalent organic group having oneor two or more 1,4-cyclohexylene groups in the main chain, 2) producinga polyimide containing a repeating unit represented by the followinggeneral formula (1) by the reaction of the purified diamine with an aciddianhydride represented by the following general formula (4) in asolvent;

wherein R₁ denotes a tetravalent organic group,

wherein R₁ and R₂ are as described above, 3) applying a solutioncontaining the polyimide to the substrate or a thin film formed on thesubstrate; and 4) drying and/or firing the applied solution containingthe polyimide at 100° C. or more and 250° C. or less to form a polyimidelayer.
 2. The method for manufacturing an optical member according toclaim 1, further comprising: 5) applying a precursor sol of aluminumoxide to the outermost surface of the laminated body; 6) drying and/orfiring the applied precursor sol of aluminum oxide at 100° C. or moreand 250° C. or less to form an aluminum oxide film; and 7) immersing thealuminum oxide film in hot water to form a textured structure formed ofplate crystals containing 70% by mole or more of aluminum oxide.
 3. Apolyimide having a repeating unit represented by the following generalformula (1), wherein 90% by mole or more of a 1,4-cyclohexylene group inthe general formula (1) has a trans form:

wherein R₁ denotes a tetravalent organic group, and R₂ denotes adivalent organic group having one or two or more 1,4-cyclohexylenegroups in the main chain.
 4. The polyimide according to claim 3, furthercomprising a repeating unit represented by the following general formula(2):

wherein R₁ denotes a tetravalent organic group, n denotes an integer inthe range of 0 to 2, R₃ to R₁₀ independently denote a hydrogen atom, ahalogen atom, a phenyl group, or a linear or cyclic alkyl, alkenyl, oralkynyl group having 1 to 6 carbon atoms, and R₁₁ and R₁₂ independentlydenote a hydrogen atom or a linear or cyclic alkyl group having 1 to 6carbon atoms.
 5. The polyimide according to claim 3, further comprisinga repeating unit represented by the following general formula (5):

wherein R₁ denotes a tetravalent organic group, R₁₁ to R₁₄ independentlydenote a hydrogen atom, a phenyl group, or an alkyl, alkenyl, or alkynylgroup having 1 to 4 carbon atoms, R₁₁ to R₁₄ may be the same ordifferent, R₁₅ and R₁₆ independently denote a phenylene group or analkylene group having 1 to 4 carbon atoms, R₁₅ and R₁₆ may be the sameor different, and n denotes an integer in the range of 0 to
 6. 6. Amethod for producing a polyimide, comprising: purifying a diaminerepresented by the following general formula (3) such that 90% by moleor more of a 1,4-cyclohexylene group in the general formula (3) has atrans form;[Chem. 6]H₂N—R₂—NH₂  (3) wherein R₂ denotes a divalent organic group having oneor two or more 1,4-cyclohexylene groups in the main chain, producing apolyimide precursor by the reaction between the diamine represented bythe general formula (3) purified and an acid dianhydride represented bythe following general formula (4) in a solvent;

wherein R₁ denotes a tetravalent organic group, producing a polyimide bythe imidization of the polyimide precursor in a solvent; and isolatingthe polyimide by removing the solvent.
 7. The method for producing apolyimide according to claim 6, wherein the polyimide precursor isproduced by the reaction between the diamine represented by the generalformula (3) purified, a diamine represented by the following generalformula (12), and the acid dianhydride represented by the generalformula (4):

wherein R₁₁ to R₁₄ independently denote a hydrogen atom, a phenyl group,or an alkyl, alkenyl, or alkynyl group having 1 to 4 carbon atoms, R₁₁to R₁₄ may be the same or different, R₁₅ and R₁₆ independently denote aphenylene group or an alkylene group having 1 to 4 carbon atoms, R₁₅ andR₁₆ may be the same or different, and n denotes an integer in the rangeof 0 to 6.